Mean

The mean or arithmetic mean of a set of numbers is obtained by adding the number and dividing the result by the 'number' of numbers. It is a key piece of information: if you randomly sample some numbers from the series, you expect them to fluctuate around the mean, and the larger the sample, the closer their average will tend to be to the mean of the series.

An alternative indicator of average is the median, the middle number if all numbers are ordered according to size. The mean and the median need not have the same value; in some cases, the difference can be quite considerable.